There have been available several kinds of trip throttle valves (so-called T and T valves). Among them, a hydraulically controlled type has also been known. In such a T and T valve with hydraulic manual exerciser, the opened state thereof is maintained by a hydraulic pressure and, in case of emergency, the valve is momentarily closed by releasing the hydraulic pressure. After such emergency shut off, such valve is to be reset for further operation. In addition, a valve body is moved manually, after the resetting, to open the valve and the valve body is maintained in its opened state by application of the hydraulic pressure to a piston within a hydraulic cylinder, the piston being connected to the valve body and normally being urged by a spring in such a direction as to close the valve. In this type of valve, if the sequence of operation is not in a proper order, the piston may cause sudden opening or rapid opening of the valve in opposition to the opening mode intended by the operator thereby creating a dangerous situation.
Therefore, it has been desired to provide an emergency trip throttle valve which avoids the possibility of an unexpected and dangerous operating situation being caused.